1. Field of the Invention
The invention relates to a system for tracing the contents of the TAG IN and TAG OUT registers in an I/O channel.
2. Description of the Related Art
The concept of tracing the operation of an I/O channel to aid in diagnoses of problems encountered by the I/O channel has been done within the I/O channel art field. Generally, this has been accomplished by tracing the contents of the TAG IN register associated with the I/O channel for every cycle of operation of the I/O channel. The contents of the TAG IN register for each cycle would be sequentially stored in a dedicated RAM which could be accessed by the operating system. When an interface control check error is detected by the I/O channel, the I/O channel freezes the channel interface and enter into a diagnostic mode to ascertain what caused the interface control check error.
While the above employed methodology of tracing part of the operation of the I/O channel has been helpful in diagnosing I/O channel interface problems, the information obtained was not sufficient to allow the diagnosis of the many errors that occur within the I/O channel.
Further, since no history is maintained for the TAG OUT register, the only set of out tags available to the system for diagnosing the problem would be those out tags stored in the TAG OUT register when the I/O channel is frozen at the time that interface control check error has been detected by the I/O channel. It has been found that there may be a delay in generating the interface control check signal generated by the I/O channel upon the detection of an interface control check error such that the previous set of out tags, than those out tags presently stored in the TAG OUT register, may have been involved in the generation of the interface control check error.